Presently, various plastic containers are used for packaging because of their advantages such as light weight, transparency and easiness of molding.
However, because an oxygen barrier property of the plastic containers is lower than these of metal containers and glass containers, the plastic containers have problems in that the contents of the containers deteriorate due to chemical oxidation and the action of aerobic bacteria.
For preventing these problems the plastic container walls have a multi-layer structure in which at least one layer is made of a resin having an excellent oxygen barrier property such as an ethylene-vinyl alcohol copolymer. In addition, there are other kinds of containers having an oxygen-absorbing layer for absorbing oxygen remaining in the containers and also oxygen gas penetrating into the containers from the outside. Oxygen gas absorbers (deoxidizer) used for forming the oxygen-absorbing layer include, for example, those mainly containing a reducing substance such as iron powder (see, for example, Japanese Examined Patent Publication (JP KOKOKU) No. Sho 62-1824).
A method in which an oxygen absorber such as iron powder is incorporated into a resin and the resulting resin composition is used as a material for forming the wall of a container used as a packaging material shows a sufficiently high ability to absorb oxygen gas, but the resulting resin composition has a color hue peculiar to the iron powder. Therefore, said method is limited in its application and cannot be used in the field of packaging in which transparency is required. Further, there have been disclosed, as a resin-based oxygen absorbing material, an oxygen absorbing resin composition comprising a carbon to carbon unsaturated bond-containing resin and a transition metal catalyst (see, for example, Japanese Un-Examined Patent Publication (JP KOKAI) No. 2001-39475, Japanese Un-Examined Patent Publication (JP KOHYO) No. Hei 8-502306 and Japanese Patent No. 3,183,704) and an oxygen absorbing resin composition comprising a resin having a cyclic olefin (cyclohexene) structure and a transition metal catalyst (in particular, a Co salt) (see, for example, Japanese Un-Examined Patent Publication (JP KOHYO) No. 2003-521552 and Japanese Un-Examined Patent Publication (JP KOKAI) No. 2003-253131). However, the former composition has a problem that the molecular chain of the resin is cleaved as the resin absorbs oxygen gas and thus generates low molecular weight organic components as an odor component. On the other hand, the latter composition comprises ring structures as the oxygen gas-absorbing sites, and accordingly it could somewhat inhibit the generation of such low molecular weight odor components, but there is a tendency that the use of such a transition metal catalyst (a Co salt) may easily result in the occurrence of reactions at sites other than the expected oxygen-absorbing sites and this in turn leads to the formation of decomposition products.